At a container terminal in a harbor, an inland area or the like, quay cranes and gantry cranes are used to load and unload containers to and from ships and trailers.
FIG. 6 is a schematic view of a harbor container terminal 30. A container 35 on a container ship 34 is loaded onto a trailer 33 by a quay crane 36, and is then loaded onto a lane 31, which is a container load block, from the trailer 33 by a gantry crane 2X. In some cases, the container 35 is transported to the destination of the load while being kept on the trailer 33.
Here, the gantry cranes 2X may be classified broadly into a rail-mounted type and a rubber-tire type. A rail-mounted gantry crane (referred to as an RMT below) moves on rails laid along the lane 31 at approximately eight km per hour to perform loading and unloading operations. Electricity to serve as power for the RMT is often supplied by connecting a cable, installed in the crane 2X, to a power supply connector 32 in the terminal.
By contrast, a rubber-tired gantry crane (referred to as an RTT below) travels on tires. Having this configuration, the RTT can easily move between lanes (change lanes), and can hence be moved easily to the lane 31 that is assigned to a lot of loading and unloading operations. To make use of the maneuverability of the RTT, power for the RTT is often electricity supplied by a diesel generator or the like provided in the RTT.
In these years, out of consideration for environment, energy sources for RTTs are increasingly switched from power generated by diesel generators, which produce exhaust gas, to shore electricity supplied from the container terminal 30 (see Patent Document 1, for example). Patent Document 1 discloses a method of supplying power to an RTT by using a cable reel, which is means for reeling and unreeling a cable, as in the case of an RMT. Using this method can reduce exhaust gas. However, although one of the advantages of RTTs is to be capable of changing lanes easily, this is difficult in the case of using the above-described method. Specifically, an on-shore power supply connector 32 connected with the cable reel is provided for each lane, and for changing lanes, the cable needs to be detached from and attached to the power supply connectors 32 of the lanes. Moreover, the power supply connectors 32 carry high-voltage electricity and have problems in safety and operability in attaching and detaching operations. To solve these problems, a power supply system has been proposed in which a power supply truck is linked to a crane to supply power to the crane through the power supply truck (see Patent Document 2, for example).
As shown in FIG. 7, a power supply system 1X described in Patent Document 2 includes a power supply truck 3X in which a cable reel and a transformer are installed. The power supply system 1X is configured to supply power to the crane 2X by converting high-voltage electricity transmitted by an on-shore power supply to low-voltage electricity by using the transformer. A cable is attached or detached for a lane change at a connection part 21 between the transformer and the crane. Since low-voltage current obtained from the conversion by the transformer flows through the connection part 21, this configuration can improve safety and operability in attaching and detaching the cable for lane changes, to some extent. Incidentally, the high-voltage electricity is defined to be in the range of 3300 to 11000 V, and the low-voltage electricity, although varying depending on country and area, is defined to be 600 V or below in Japan, for example.
In addition, the power supply truck 3X has a configuration of being towed by the crane 2X by use of a linkage mechanism 4X linking the crane 2X and the power supply truck 3X, and travels on a power-supply-truck traveling rail 23 laid on a lane 31, by following the crane 2X. Incidentally, the power supply truck 3X is self-propelled by including therein a driving system in some cases, but often has a configuration of being linked to the crane 2X with the linkage mechanism 4X and towed by the crane 2X in consideration of the cost.
Here, the linkage mechanism 4X needs to be a flexible linkage structure 4X in such a manner that vibrations and the like caused along with travel of the crane 2X would not affect the power supply truck 3X. For this purpose, a universal joint, a link mechanism or the like is used for the linkage mechanism 4X (see FIG. 3 and FIG. 5 in Patent Document 2, for example).